Acoustic wave touch actuated switch with feedback

ABSTRACT

An acoustic wave switch includes a substrate with an acoustic wave cavity formed therein such that the mass per unit area of the acoustic cavity is greater than the mass per unit area of the substrate adjacent the cavity. A transducer is mounted on the acoustic cavity for generating an acoustic wave that is substantially trapped in the cavity. A touch on the touch surface of the acoustic wave cavity absorbs acoustic wave energy and produces a detectable change in the impedance of the transducer. Various feedback mechanisms can be employed to provide a user with a tactile, audible and/or visual response indicating actuation of the switch by a touch.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.09/766,000 filed Jan. 18, 2001 now abandoned entitled ACOUSTIC WAVETOUCH ACTUATED SWITCH.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

N/A

FIELD OF INVENTION

The present invention relates to an acoustic wave touch actuated switchand more particularly to such a switch having an acoustic cavity thatsubstantially traps acoustic wave energy so as to provide a high Qswitch.

BACKGROUND OF THE INVENTION

There is a substantial need for finger touch actuated switches that arerugged and explosion proof, operate in the presence of liquids, have lowpower consumption, withstand aggressive sterilization procedures and areinexpensive. Known switches that attempt to meet these needs but failinclude the following. A Qprox switch made by Quantum Research Groupsenses the presence of touch through a charge transfer effect. Thisswitch is sensitive to conductive fluids and/or an ionizing atmosphereand can be made inoperable thereby. Further, the enclosure through whichtouch is sensed cannot be made of an electrically conducting material,so that metals and the like cannot be used. Piezoelectric switches suchas supplied by Schurter or Wilson-Hurd, operate by transferring fingerpressure via a metal overlay to a piezoelectric element which generatesa voltage when compressed. This type of switch is expensive compared toa standard membrane switch and shares the disadvantages of membraneswitches in that holes in the housing or enclosure are required toaccommodate the switch. Further, the metal overlay is necessarily thin,so that the piezoelectric element is relatively unprotected againstblows to the overlay. Another type of switch shown in U.S. Pat. No.5,149,986 is based on the absorption of sound in a glass, ball-shapedbutton when the button is touched. In operation, a transducer sendssound waves into the glass balls and then receives back the echoes in asonar type fashion. A circuit analyzes the echoes to determine whetherthe echoes have been reduced indicating a touch. This type of switch isrelatively expensive and again requires openings in the housing orenclosure in which the switch is to be mounted.

An acoustic wave switch such as shown in U.S. Pat. No. 5,673,041includes an ultrasonic piezoelectric transducer mounted on a surface ofa substrate opposite a touch surface of the substrate. The transducergenerates an ultrasonic wave that propagates in a direction across thethickness of the substrate to the touch surface and reflects off of thetouch surface back to the transducer. The ultrasonic wave appears to bea compression wave. A touch on the touch surface changes the acousticreflectivity of the surface and changes the impedance of the transducer.The acoustic energy in this switch is not confined and spreads out intothe plane of the substrate. As such, the ratio of the stored energy tolost or dissipated energy over a complete cycle, referred to as the Q ofthe switch, is inherently low and an extremely complex touch detectioncircuit is required to discriminate between a touch and the absence of atouch. Moreover, the use of compression waves in this switch isundesirable due to their sensitivity to liquids and other contaminantswhich can render the switch inoperable.

Also known are acoustic wave touch panels that employ reflectivegratings or arrays to reflect portions of an acoustic wave across atouch surface along parallel paths of differing lengths. These devicesuse a transparent substrate that can overlay a display to provide atouch screen or the like. Examples of such touch sensors are shown inU.S. Pat. Nos. 4,645,870 and 4,700,176 which utilize surface acousticwaves. These systems are undesirable, however, because surface acousticwaves are sensitive to liquids, sealing compounds and other contaminantsthat can render the panel inoperable and difficult to seal effectively.Another acoustic wave touch panel using reflective arrays is shown inU.S. Pat. No. 5,177,327. This touch panel uses shear waves and inparticular the zeros order horizontally polarized shear wave. Althoughthis touch position sensor is insensitive to liquids and contaminants,touch position sensors that use reflective gratings or arrays and theassociated touch detection circuitry are, in general, too expensive touse for an individual switch or for a small number of switches on apanel. Moreover, because the shear wave transducer in this latter systemis mounted on a side of the panel to generate a shear wave thatpropagates in the plane of the substrate, an opening in the enclosure orhousing is required to accommodate the panel. U.S. Pat. No. 5,573,077also uses zeros order horizontally polarized shear waves, but instead ofreflective gratings, discrete transducers are used to propagate theshear waves along parallel paths extending across the substrate.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, the disadvantages of priorswitches as discussed above have been overcome. In accordance with thepresent invention, acoustic wave energy is substantially trapped in anacoustic cavity so as to provide an acoustic wave switch with a high Q.Because the Q of the switch is high, a touch can be detected withextremely simple circuitry.

More particularly, the acoustic wave switch of the present inventionincludes a substrate with an acoustic wave cavity formed therein suchthat the mass per unit surface area of the acoustic cavity is greaterthan the mass per unit surface area of the substrate adjacent thecavity. An acoustic wave transducer is mounted on the acoustic cavity togenerate an acoustic wave that is substantially trapped in the acousticcavity. Even a light touch on a touch surface of the cavity produces achange in the impedance of the transducer that is easily detectable by asimple, low cost circuit.

In one embodiment of the switch, a thin mesa or plateau is formed on thesubstrate to define the acoustic cavity. Specifically, the acousticcavity is formed of the mesa and the portion of the substrate below themesa. The mesa may be formed on the touch surface side of the substrateor on a side of the substrate opposite the touch surface. The mesa canbe an integral part of the substrate by mechanically or chemicallymachining the substrate. Alternatively, the mesa can be formed byadhering material to the substrate in a localized area to define theacoustic cavity. In the latter embodiment, the material forming the mesamay be the same as or a different material than the material forming thesubstrate. The substrate may be formed of metal, plastic, glass orceramics, etc., capable of supporting a resonant acoustic wave.Moreover, the switch can use a wall of a housing or device enclosure asthe substrate so that at least a portion of the switch, i.e. theacoustic cavity is an integral part of the housing wall. As such, noholes have to be formed in the housing or enclosure to accommodate theswitch, eliminating sealing problems and providing a switch which isextremely rugged.

In a preferred embodiment, a shear wave transducer is mounted on theacoustic cavity so as to generate a shear wave in the plane of thesubstrate and parallel to the touch surface. The shear wave, however,has a higher order mode than the zeros order mode so that the wave canbe substantially confined to or trapped in the acoustic cavity. Itshould be appreciated, however, that acoustic waves, capable of beingsubstantially trapped in an acoustic cavity, other than a shear wave canbe used in accordance with the present invention as well.

The acoustic wave switch of the present invention is low-cost, rugged,explosion proof, operates with simple, low-powered electronics andcontinues to function in the presence of ionizing environments, liquidsand other contaminants. These and other objects, advantages and novelfeatures of the present invention, as well as details of an illustratedembodiment thereof, will be more fully understood from the followingdescription and drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a top view of a panel having a number of acoustic waveswitches formed therein in accordance with the present invention;

FIG. 2 is a perspective view of the back of the panel of FIG. 1illustrating the substrate, mesas and associated transducers forming theacoustic wave switches;

FIG. 3 is a side cross-sectional view of an acoustic wave switch ofFIGS. 1 and 2 illustrating the acoustic cavity of the present invention;

FIG. 4 is a top view of the acoustic wave switch of FIG. 3 illustratingthe displacement of the transducer and the direction of propagation of ashear wave in the plane of the substrate;

FIG. 5 is a side cross-sectional view of the acoustic wave switchillustrating the displacement of a first order mode shear wave in they-x plane;

FIG. 6 is a side cross-sectional view of the acoustic wave switchillustrating the displacement of a third order mode shear wave in they-x plane;

FIG. 7 is a cross-sectional view of the acoustic wave switchillustrating the displacement of a shear wave having m=0 in the y-zplane;

FIG. 8 is a cross-sectional view of the acoustic wave switchillustrating the displacement of a shear wave having m=2 in the y-zplane;

FIG. 9 is a schematic diagram of a touch detection circuit for theacoustic wave switch of FIGS. 1-3;

FIG. 10 is a cross-sectional view of an acoustic wave switch inaccordance with the present invention having a depressed area indicatinga touch region;

FIG. 11 is a cross-sectional view of an acoustic wave switch inaccordance with the present invention having a raised area indicating atouch region;

FIG. 12 is an acoustic wave switch having a mesa formed on the touchsurface;

FIG. 13 is a cross-sectional view of an acoustic wave switch with anacoustic wave absorbing switch actuator to provide feedback to a userthat the switch has been actuated;

FIG. 14 is an illustration of the acoustic wave switch of FIG. 3 withthe switch actuator in the actuated position;

FIG. 15 is an illustration of a number of acoustic wave switches of thetype shown in FIG. 11 with an overlay;

FIG. 16 is a graph illustrating the change in the transducer's impedanceat peak resonance, in the absence of a touch and in the presence of atouch;

FIG. 17 is a perspective view of the acoustic wave switch with acircular mesa;

FIG. 18 is a cross-sectional view of the acoustic wave switch of FIG. 17with the transducer mounted on a surface of the substrate opposite thecircular mesa;

FIG. 19 is a perspective view of the acoustic wave switch with acircular mesa defined by a moat in the substrate;

FIG. 20 is a perspective view of the acoustic wave switch with a domeshaped mesa surrounded by a moat in the substrate; and

FIG. 21 is a cross-sectional view of the acoustic wave switch of FIG. 20illustrating the transducer on a surface of the substrate opposite thedome.

FIG. 22 is a cross-sectional view of a panel such as illustrated in FIG.2 with a mechanism for providing feedback to a user;

FIG. 23 is a cross-sectional view of a panel such as illustrated in FIG.2 with another embodiment of a mechanism for providing feedback to auser;

FIG. 24 is a cross-sectional view of a panel such as illustrated in FIG.2 with a further embodiment of a mechanism for providing feedback to auser;

FIG. 25 is a cross-sectional view of a panel such as illustrated in FIG.2 with still another embodiment of a mechanism for providing feedback toa user;

FIG. 26 is a cross-sectional view of a panel such as illustrated in FIG.2 with a further embodiment of a mechanism for providing feedback to auser;

FIG. 27 is a cross-sectional view of a panel such as illustrated in FIG.2 with another embodiment of a mechanism for providing feedback to auser; and

FIG. 28 a cross-sectional view of a panel such as illustrated in FIG. 1with a further embodiment of a mechanism for providing feedback to auser.

DETAILED DESCRIPTION OF THE INVENTION

A touch panel as shown in FIGS. 1 and 2 has a number of acoustic waveswitches in accordance with the present invention formed in thesubstrate 14 of the touch panel. Each acoustic wave switch 12 hasrespective indicia 16 formed on a top surface 18 of the panel. Theindicia 16 identifies the position of a switch 12 and a switch actuationtouch surface which are centrally located in the indicia 16. The indicia16 can be formed in a number of different ways as described in detailbelow.

As shown in FIG. 2 and in more detail in FIG. 3, each acoustic waveswitch 12 has an associated acoustic wave cavity 20 that extends throughthe thickness b_(s) of the substrate 14. The acoustic wave cavity 20 isformed in the substrate 14 such that the mass per unit surface area ofthe acoustic wave cavity 20 is greater than the mass per unit surfacearea of the substrate adjacent the cavity. In one embodiment, the massper unit area of the substrate in the switch region is increased to formthe acoustic wave cavity 20 by forming a thin plateau or mesa 22 on asurface of the substrate that is parallel to the plane of the substrateand/or a touch surface 28. The mesa 22 can be formed on a back surface24 of the substrate opposite the touch surface 28 of the acoustic cavityas shown in FIG. 3. Alternatively, the mesa 22 can be formed on theswitch actuation touch surface 28 as shown in FIG. 12. A transducer 26is mounted on a surface 30 of the acoustic wave cavity 20 to generate anacoustic wave that is substantially trapped or localized in the cavity20. Although the transducer 26 is shown in FIG. 3 as mounted on the mesa22, if the mesa 22 is formed on the touch surface 28 of the substrate,the transducer 26 is mounted directly on the substrate surface 29 of theacoustic cavity opposite the mesa as shown in FIG. 12 so that thetransducer is on the backside of the substrate.

The acoustic wave switch 12 of the present invention can use any type ofacoustic wave capable of being substantially trapped in an acoustic wavecavity. For simplicity, the switch 12 will be described for a preferredembodiment that uses a shear wave in a direction that is in the plane ofthe substrate, wherein the shear wave energy extends in a directionperpendicular to the substrate plane, i.e. through the thickness of thesubstrate. A shear wave is advantageous because it is insensitive toliquids and other contaminants on the touch surface 28 of the switch 12.Because the fundamental or zeros order mode of a horizontally polarizedshear wave cannot be substantially trapped, higher order shear wavemodes are used in accordance with the present invention. It should beappreciated that because the acoustic wave used in accordance with thepresent invention is trapped, the wave is a standing wave. A standingwave has a number of advantages over an acoustic wave that propagates ortravels along a path in a substrate. For example, propagating waves arenot confined to the main path of propagation but can diffract off of themain path complicating touch detection. This is opposed to a standingwave which by its nature is confined to the area of the cavity. Becausethe acoustic wave is confined, touch detection is easily accomplished.Further, the wave energy of a propagating wave is not stored at anylocation along the path. Once the wave passes a point along the path,the wave is gone. this makes timing and control critical for touchdetection with propagating waves. There are no timing or control issueswith a standing wave because the wave energy is stored in the cavity.Moreover, a propagating wave is not a resonating wave. As such, the waveenergy decays at it travels. A standing wave is resonant so that thewave is reinforced and prolonged. As a result, the standing wave has amuch greater amplitude than a wave that is not confined.

For a shear wave generated by the transducer 26 and having a harmonicmode, n greater than or equal to 1, the thickness of the cavity b_(c)should be greater than ½ λ, where λ is the wavelength of thefundamental, zeros order mode. For shear waves having a harmonic mode ofn≧1, separate cutoff frequencies exist for the acoustic cavity 20 andthe adjacent region of the substrate. These cutoff frequencies,designated f_(c) and f_(s) respectively, determine the frequency rangein which standing waves, and hence resonance, is possible. For wavefrequencies below f_(c), no waves propagate. For wave frequenciesbetween f_(c) and f_(s), standing waves can form because of reflectionsat the acoustic cavity boundaries. At wave frequencies above f_(s), thewaves will not be substantially trapped within the acoustic cavity 20and will propagate throughout the substrate 14. Thus, at frequenciesabove f_(s), resonance in the acoustic cavity 20 is suppressed due tosubstantial leakage of acoustic energy into the surrounding areas in thesubstrate 14. The cut-off frequencies f_(c) and f_(s) are given by thefollowing formulas.

${\begin{matrix}{f_{c} = \frac{{nV}_{s}}{2b_{c}}} & {f_{s} =}\end{matrix}\frac{{nV}_{c}}{2b_{s}}}$Where b_(c) is the thickness of the acoustic cavity 20; b_(s) is thesubstrate thickness in the area adjacent the acoustic cavity; V_(s) isthe velocity of the zeros order mode shear wave in the substrate; V_(c)is the velocity of the zeros order mode shear wave in the cavity and nis the order of the harmonic mode of the generated shear.

In a preferred embodiment, the cavity 20 is operated in only a singlemode. To accomplish this in practice, the geometry of the acousticcavity 20 is such that the ratio of the length to thickness of thecavity satisfies the following equation where the length is designatedas 2 a.

$\frac{2a}{b_{c}} \leq {\frac{1}{n}\sqrt{\frac{2b_{s}}{h_{c}}}}$Where h_(c) is the height of the mesa 22, i.e. h_(c)=b_(c)−b_(s).Similarly, the width w, of the acoustic cavity should satisfy the samerelationship as follows.

$\frac{w}{b_{c}} \leq {\frac{1}{n}\sqrt{\frac{2b_{s}}{h_{c}}}}$

Further, the transducer 26 is positioned along a center line of thecavity.

FIGS. 4-7 illustrate the peak displacement of the wave motion in theacoustic cavity for a transducer 26 that is mounted on the acousticcavity such that the length of the transducer 26 extends along a centerline of the acoustic cavity surface in the X direction. In particular,as seen in FIG. 4 for a shear wave transducer having displacement in theX direction, the shear wave generated in the acoustic cavity propagatesin a direction that is in the plane of the substrate (the X-Z plane) asopposed to across the thickness thereof. The shear wave has adisplacement component in the y direction designated U_(y) which isillustrated in FIG. 5 for the harmonic mode, n=1 and in FIG. 6 for theharmonic mode n=3. It has been found that a harmonic mode of order n=1is preferred for thin substrates 14 whereas the harmonic mode n≧3 ispreferred for thicker substrates. FIG. 7 illustrates the peakdisplacement of the wave in the y-z plane for an inharmonic mode of m=0;whereas FIG. 8 illustrates the peak displacement of the wave in the y-zplane for an inharmonic mode of m=2.

It should be appreciated that the cavity may also be operated in morethan one mode in accordance with the present invention. Further, thetransducer need not be placed along a centerline of the cavity. Forexample, the transducer may be placed on the cavity adjacent to an edgethereof. The transducer may also be placed on the cavity but spaced froman edge thereof. The distance from the transducer to the cavity edge canbe chosen to selectively cancel modes.

The acoustic wave cavity of the present invention has a high Q such ason the order of 400. The amount of energy absorbed by touching thesurface 28 of the acoustic cavity in the 1-5 MHz range is notparticularly frequency sensitive. A light touch on the surface 28reduces the Q by a factor of 2.5, i.e. from 400 to 160. As such, byincorporating the transducer into a very basic and simple circuit, atouch on the acoustic cavity touch surface 28 can be easily detected soas to generate a signal indicating actuation of the switch. As can beseen in FIG. 16, a touch on the surface 28 of the acoustic cavityabsorbs acoustic energy therein resulting in an easily detectable dropin impedance. For an untouched panel, the impedance of the transducer isat a peak, R_(P). In the presence of a touch, the impedance of thetransducer drops to a level R_(m). below a threshold R_(t) that can beset as discussed below. By incorporating the transducer 26 into anoscillator circuit as described below with reference to FIG. 9, the dropin impedance indicating a touch can be readily detected. In the absenceof touch, the circuit oscillates and in the presence of a touch,oscillation stops. By detecting the state of oscillation, a signal isgenerated indicating the occurrence of a touch actuating the switch 12.

FIG. 9 is a diagram of an extremely simple touch detection circuit for apanel 10 having a number of acoustic wave switches 12. Each transducer26 associated with a respective acoustic switch 12 is coupled to amultiplexer 40 which sequentially couples a transducer and therefore itsassociated acoustic switch 12 to an oscillator 42. The oscillator 42includes an operational amplifier 44 having a gain-bandwidth product of60 MHz. The operational amplifier 44 has two feedback paths. Thefeedback path 46 connected from the output of the operational amplifier44 to the negative input terminal thereof sets the static voltage gainto approximately 1.5 through a 47 kΩ resistor 48, a 4.7 kΩ resistor 49and an 82 kΩ resistor 50. The voltage gain at resonant frequency isapproximately 11 because the resistor 50 is bypassed by the 200 pfcapacitor 52. The second feedback path of the operational amplifier 44connects the output thereof to the positive input terminal of theoperational amplifier 44 via a 39 kΩ resistor 54 and a 200 pf capacitor56. The amplifier 44 is connected to a second operational amplifier 58that detects the state of the oscillator 42 through a 5.6 kΩ resistor 60and a pair of diodes 62 and 64.

It can be assumed that the transducer impedance is purely resistive atanti-resonance. With this assumption, the value of the resistor 54 ischosen such that a voltage that exceeds 1/A_(v) of the output, whereA_(v) is the gain of the oscillator at resonant frequency (in this caseA_(v)=11), is fed back to the positive terminal of the operationalamplifier 44. Under this condition, the operational amplifier 44 willoscillate. If the resistance of the transducer 26 coupled to theoperational amplifier 44 is designated R_(p) and resistor 54 isdesignated as R_(f) then the condition for oscillation is as follows.

$\frac{R_{f}}{R_{p}} \leq \left( {A_{v} - 1} \right)$

More particularly, the value of the resistor 54, R_(f), is selected suchthat the acoustic cavity 20 will cause the oscillator 42 to oscillate inthe absence of a touch. A touch on the surface 28 of the acoustic cavity20 will cause the transducer impedance to drop so that the oscillator 42stops oscillating. The operational amplifier 58 is biased so that theinput level matches the quiescent output of the oscillator circuit 44with diodes D1 and D2 acting as threshold switches. When the operationalamplifier 44 is oscillating, the operation amplifier 58 has a highoutput whereas in the quiescent condition the output of the operationalamplifier 58 is low or zero. Thus, the operational amplifier 58generates a low or zero signal in the presence of a touch and in theabsence of a touch the output is high. It should be appreciated thattouch detection circuits other than as depicted in FIG. 9 may be used inaccordance with the present invention as well.

In a preferred embodiment, the transducer 26 is mounted on a surface ofthe acoustic touch panel such that the surfaces 71 and 72 of thetransducer 26, across which a voltage is applied to excite thetransducer, are parallel to the plane of the substrate 14 and/or theplane of the touch surface 28 of the acoustic cavity 20. It has beenfound that mounting the shear transducer in this manner generates ashear wave having a harmonic mode with n≧1 without generating thefundamental or zeros order mode of the shear wave. This is opposed tothe manner in which shear wave transducers are typically mounted on asubstrate to generate a shear wave in the plane of the substrate. Thetypical arrangement mounts the transducer such that the surfaces acrosswhich the voltage is applied to excite the transducer are perpendicularto the plane of the substrate and touch surface, for example on a sideof the substrate as opposed to the top or the bottom of the substrate asin the present invention. It has been found, however, that shear wavesof higher order modes, i.e. n≧1, will be generated in the plane of thesubstrate, as depicted in FIG. 4, without generating a substantialfundamental mode shear wave by mounting the transducer such that thesurfaces 71 and 72 thereof are parallel to the plane of the substrateand/or touch surface. It should be appreciated, however, that othermounting positions of the transducer 26 will generate the desired higherorder modes of the shear wave without generating a substantialfundamental shear wave mode. For example, the transducer 26 may bemounted on a side 74 of the mesa where the side is appropriately angledso that it is not perpendicular to the plane of the substrate. Thismounting method will work but results in a more complicatedmanufacturing process for the acoustic wave switch 10.

Further, although it is preferred that the transducer be mounted along acenter line of a surface of the acoustic wave cavity as discussed above,the acoustic wave switch 12 will work for other transducer mountingpositions, for example, on surface 30 but adjacent an edge 76 thereof.The preferred shear wave transducer materials are Lead Zirconium, Titanate (PZT) types and specifically PZT4D, PZT5A and PZT8 supplied, forexample, by Morgan Matroc Transducer Products Ltd. These transducers arepreferred due to their combination of high coupling factors, lowacoustic and electrical losses and impedance levels.

For most switch applications, the acoustic wave cavities 20 operatebetween 1 and 3 MHz so that the minimum wavelength is approximately 40mils. At these wavelengths, bonding of the transducer is not aparticularly critical element because standard assembly proceduresproduce bond lines that are less than 0.2 mil thick. The adhesive,typically an epoxy that is operable over a wide temperature range,should be fairly rigid to reduce acoustic wave losses and provide bondshear strengths high enough to tolerate stresses at the epoxy interfacesdue to differential thermal expansion rates between the material of thetransducer 26 and the material of the substrate 14 or mesa 22 onto whichthe transducer is mounted. A conducting epoxy is not necessary. It hasbeen found that reliable, low impedance bonds do not require aconducting epoxy. This is advantageous because most conducting epoxieshave greater acoustic losses than non-conducting epoxies. A suitableepoxy is, for example, Epotek 301 and 301-2 manufactured by EpotekCorporation which operate over a temperature range of at least −40° C.to 85° C.

A number of different methods can be used for connecting the transducer26 to the touch detection circuit. For example, wires can be solderedonto the transducer. If this method is used, the amount of solder on thetransducer should be minimized since solder is a significant absorber ofacoustic energy and will reduce the Q of the switch 12. Further, thewire should be aligned along the transducer in the shear direction tominimize wire flex which can be a source of acoustic losses. A preferredmethod uses a “Zebra Strip” manufactured by FujiPoly America CorporationSeries 5000 silver zebra connector for example. The zebra connector is arubbery material that conducts current in the thickness direction. Inaccordance with this method, the zebra connector is interposed betweenthe transducer 26 and conductive pads formed in the conductor board forthe touch detection circuitry such that the pads are aligned with thetransducer. When vertical pressure is applied, a connection is formedbetween the transducer and the pads via the zebra strip connector. Inthis method, the printed circuit board may be directly mounted over themesa 22. In a further embodiment, conducting silicones are used toconnect the transducer 26 to the touch detection circuitry.

The substrate and thus the acoustic wave cavity can be formed of anymaterial such as metal, plastic, glass, ceramic, etc., in which anacoustic wave can propagate. If the substrate on which the transducer ismounted is metal, it has been found that an electrical lead does notneed to be formed on the bottom surface 71 of the transducer in order toconnect the transducer to ground. The bonding layer between thetransducer 26 and the surface of the acoustic wave cavity is so thinthat the transducer can be connected to ground via the metal surface onwhich the transducer is mounted.

The mesas 22 can be formed integrally with the substrate as shown inFIG. 3 by mechanical machining or chemical processing such as milling,die-casting, stamping, sandblasting or etching, etc., the substrate toform the raised area of the mesa 22 having a greater mass per unit areathan the adjacent area of the substrate surrounding the mesa.Alternatively, as shown in FIGS. 10-12, the mesa 22 can be formed byadding a material in a localized area defining the length and width ofthe acoustic cavity. The material may be added to the substrate to formthe mesa by plating, thick film screening or firing frit or the likeonto the substrate. Small decals may also be adhered to the substrate tovery inexpensively form the mesas 22. The material forming the mesa inthis embodiment can be the same as or different than the materialforming the substrate 14. For transparent substrate materials, the mesas22 can be formed with decals of a contrasting color and bearing indiciato identify a particular switch, i.e. touch position. The thickness orheight h_(c) of the mesa 22 is very thin. For example, a 1/16 of an inchthick aluminum plate having a typical shear wave velocity of 124.5 milsper microsecond has a cavity cutoff frequency that is very close to 1MHz. Mesas step heights h_(c), of 3 mils ±1 mil can readily be machined,stamped, sandblasted or the like into the aluminum. In general, it isdesirable to keep the mesa height h_(c) as low as possible even if theratios of cavity length to cavity thickness and cavity width to cavitythickness satisfy the above described cavity geometry conditions. Thisis because those equations assume that the boundary conditions acrossthe cavity-substrate boundary can be matched with a singleanti-symmetric mode. In practice, this cannot be accomplished and somefundamental mode energy is generated which cannot be trapped. As such,the mesa height or step height should be minimized. In practice, it isdesired that the mesa height h_(c) be less than or equal to 10% of theacoustic cavity thickness and preferably h_(c) is less than or equal to5% of the acoustic cavity thickness. Along with the length and widthrequirements of the cavity, the height requirement of the mesa providessatisfactory conditions for operation in substantially a single modetrapped resonance.

Although the mesa 22 shown in the drawings of FIGS. 2-8 and 10-15 isdepicted as rectangular, resulting in a rectangular cavity, other shapescan be used as well. For example, FIGS. 17-19 illustrate circular mesasand FIGS. 20-21 illustrate a dome mesa. For an acoustic wave switch 12with a circular mesa 22 as shown in FIGS. 17-19, the transducer 26 ispreferably placed along a diameter of the circular mesa in anyorientation. For a circular mesa, the transducer 26 need not extendacross the entire width of the mesa so that the transducer length can beless than the mesa width or diameter. Preferably, however, the ratio oftransducer length to mesa diameter is 67% or greater. The transducer 26can be positioned on the circular mesa as shown in FIGS. 17 and 19.Alternatively, the transducer 26 can be positioned on a surface oppositethe circular mesa 22 as shown in FIG. 18. In this embodiment, the mesa22 identifies the switch position. Because the mesa 22 is circular, itmore closely matches the contact area of a finger than other mesashapes. Further, because the circular mesa is isoperimetric, i.e. thelargest area is enclosed for a given perimeter length, a greater packingdensity can be achieved than with mesas of other shapes.

FIGS. 19 and 20 illustrate mesas 22 that are formed by removing materialfrom the substrate so as to form a moat 77 surrounding the mesa 22. Inorder to acoustically isolate the mesa 22 defined by a moat 77, the moatwidth is preferably greater than or equal to 2 times the thickness ofthe acoustic cavity 20 or greater than or equal to the wavelength λ ofthe acoustic wave that is trapped in the cavity 20. It should beappreciated that the moat 77 may define mesas of shapes other thancircular such as rectangular, square, etc. as well.

FIGS. 20 and 21 illustrate a convex or dome shaped mesa 22. The convexmesa forms a tactile switch without moving parts. Moreover, because theboundary of the acoustic cavity is defined by a gradual slope as opposedto an abrupt edge, the acoustic switch is more tolerant of transducermisalignment. The mesa 22 of FIGS. 20 and 21 is formed by removingmaterial from the substrate to form the moat 77 and to contour the shapeof the convex mesa 22. In this embodiment, the transducer is preferablymounted on a flat surface of the acoustic cavity, i.e. on the substratesurface opposite the dome 22 as shown in FIG. 21. It should be apparentthat the dome shaped mesa 22 need not be surrounded by a moat.

The size of the acoustic cavity 20 defined by the length and width orthe diameter thereof can be much smaller than the area identified by theindicia 16 indicating the position of a switch 12 so as to minimize thesize of the transducer 26 and thus reduce the cost of the acoustic waveswitch 12. It has been found that a finger does not have to completelycover the touch surface 28 of the acoustic cavity 20 in order to absorbsufficient amount of energy to be easily detected.

Various methods can be used to indicate the position of the switch 12.The indicia 16 indicating the position of the switch 12 can be formedwith polyurethane paint. These paints do not drastically reduce the Q ofthe cavity. For a metal substrate 14 such as aluminum, anodization canprovide striking contrasts. The coating is essentially aluminum oxidewith a dye incorporated into the oxide via additives in an anodizationbath. This method creates rugged indicia. Other methods that can beemployed to create the indicia to identify the switch position arelaser, mechanical or chemical engraving. With this method, an outline 80of the switch position is preferably formed in an area outside of theacoustic cavity. Although the numeral indicia 81 is at least in partformed in the touch surface 28 of the acoustic cavity 20 the removal ofthe slight amount of mass to form the numeral indicia 81 does not effectthe operation of the acoustic cavity 20. For glass and ceramicsubstrates 12, the indicia identifying the switch position can bepainted on the substrate. In the case of glass and other transparentsubstrates, the indicia can be formed on the back surface of thesubstrate opposite the touch surface so that a coating providing theindicia is not exposed. The switch positions can also be identified byeither a depressed or raised region formed in the substrate as discussedbelow.

As shown in FIG. 10, the indicia identifying the position of the switch12 is a depressed region 90. The touch responsive surface 28 of theacoustic wave cavity 20 is generally centered in the depressed region90. Because in practice, not all of the acoustic wave energy will betrapped within the cavity 20, it is preferred that the walls 92 of thedepressed region be spaced from the walls 94 of the acoustic cavity 20by a distance that is greater than or equal to 0.6 b_(c)/n. As can beseen from FIG. 10, with this minimum spacing, even though the thicknessof the substrate outside of the depressed region is greater than thethickness of the acoustic cavity 20, the acoustic cavity 20 still has amass per unit area greater than that of the substrate 14 adjacent to thecavity so as to enable the acoustic wave energy to be substantiallytrapped in the cavity 20. In FIG. 11, the indicia identifying the switchposition 12 is a raised region 96. Again in this embodiment, the sidewall 97 of the raised region 96 should be spaced a distance from theedge 94 of the acoustic cavity 20 by a distance that is greater than orequal to 0.6 b_(c)/n so as to prevent leaked acoustic energy at the edge97 from effecting the operation of the cavity 20. In the embodiment inFIG. 12, the raised surface 96 indicating the position of the switch 12also forms the mesa 22 with the transducer 12 mounted directly on theback surface 29 of the acoustic cavity 20 and substrate 14. In thisembodiment, the minimum spacing between the edge of one mesa 22 and anadjacent mesa is 0.6 b_(c)/n.

Feedback to the user that the switch 12 has been actuated can beprovided by a number of different methods. For example, the detectioncircuitry can actuate a beeper or the like to provide sound feedback tothe user that a touch has actuated the switch 12. Alternatively, thecircuit can actuate a light or the like to provide visual feedback.Tactile and audible feedback can be provided in accordance with theembodiments depicted in FIGS. 13-15. In this embodiment, an acousticwave absorbing switch actuator 100 is positioned over the touch surface28. The switch actuator 100 is formed of a metal or plastic dome 102 orthe like with an acoustic wave absorbing material or coating 104 on theinner surface thereof. The acoustic wave absorbing material 104 may be aurethane rubber or the like. When the actuator 100 is depressed by afinger as depicted in FIG. 14, the acoustic wave absorbing material 104touches the touch surface 28 of the switch 12 so as to actuate theswitch. Tactile feedback is provided when the touch surface 28 iscontacted by the switch actuator 100. Further, when the dome deforms, aclicking sound may be produced to provide an audible feedback. Anoverlay 106, as depicted in FIG. 15, and formed of silicone rubber orthe like can be positioned over the switch actuators 100 to provide asmooth top surface.

FIGS. 22-25 illustrate alternative embodiments for providing feedback tothe user that the switch has been actuated. In FIGS. 22 and 23, apolymer sheet 120 which may be made, for example of a molded silicone,overlays the substrate 14. The sheet 120 is molded with domes 122 formedtherein. The domes 122 are positioned on the sheet 120 so that each domeis above a respective acoustic switch formed by the mesa 22 andtransducer 26 on a substrate surface opposite the sheet 120. An acousticwave absorbing material 124 as shown in FIG. 22 is mounted or coated onthe concave surface of the dome facing the touch surface 28 of theswitch so that when the dome is depressed the acoustic wave absorber 124contacts the touch surface 28 of the switch. In FIG. 23, instead of anindividual acoustic wave absorber 124 associated with each dome 122, asheet of acoustic wave absorbing material directly overlays thesubstrate 14 and is disposed between the substrate 14 and the polymersheet 120 with molded domes. When an individual dome is pressed,exerting a force or pressure on an area of the absorbing sheet 120overlaying the acoustic cavity, the impedance of the transducer changesindicating actuation of the switch. FIGS. 24 and 25 illustrate differentembodiments similar to FIGS. 22 and 23 respectively, but the sheet 120′is formed of metal with truncated domes 122′ stamped therein. When thedomes 122′ are depressed actuating the switch, the domes click providingaudible as well as tactile feedback. It is noted that the acousticabsorber 124 of FIGS. 22 and 24 may be a polymer with embedded magneticparticles to further aid in providing an audible click and tactilefeedback.

FIG. 26 provides tactile feedback of switch actuation using a rocker 132having a magnet 130 mounted on a surface of the rocker 132 on a firstside of a pivot point 133 and having an acoustic wave absorber 134mounted on a surface of the rocker 132 on a second side of the pivotpoint 133. The magnet 130 is held against a substrate 14 formed of asteel plate or the like, so as to maintain the switch in an punctuatedstate. When the force on the rocker 132 above the absorber 134 overcomesa threshold, the rocker 132 pivots about the point 133 so that theacoustic wave absorber 134 contacts the touch surface 28 of the acousticwave switch 12 so as to actuate the switch. Upon release of the rockerend above the absorber, the magnet 130 is attracted to the steelsubstrate 14 so as to return the rocker 132 to the punctuated switchposition.

FIG. 27 illustrates another embodiment that provides feedback of switchactuation using a plunger 140 that extends through an aperture 144 in asteel plate 146. The plunger is held in an punctuated position above thetouch surface 28 of an acoustic wave switch 12 by magnets 142 that aremounted on a flange 148 of the plunger. In the punctuated position, themagnets 142 are held against the steel plate 146 which is spaced abovethe substrate 14 by a sufficient distance so that an acoustic waveabsorber 149 mounted on an end of the plunger 140 does not contact thetouch surface 28 in an punctuated switch position. When a force isapplied to the top of the plunger 140, overcoming the holding force ofthe magnets 142, the plunger moves downward so that the absorber 149contacts the touch surface 28 actuating the switch. When the plunger 140is released, the magnets 142 are attracted back to the steel plate 146to return the plunger back to the punctuated position as shown in FIG.27.

FIG. 28 illustrates an embodiment to provide feedback with no mechanismoverlying the touch surface 28. In this embodiment, a solenoid 150 ismounted on a back surface of the substrate 14. When a touch on a surface28 is detected as discussed above, current is applied to the solenoid150. When current is applied to the solenoid 150, a rod 152 of iron,steel or the like, forming a striker is moved upward hitting thesubstrate 14 with sufficient force so that a finger on a nearby touchsurface 28 feels motion or vibration of the substrate 14. The impact ofthe rod 152 against the substrate 14 can also provide audible feedbackas well if desired. It is noted that the substrate 14 acts as a loadspreader so that the substrate motion on impact by the rod 152 is notlocalized. As such, one solenoid can provide feedback for a number ofacoustic wave switches formed on the substrate 14.

Because the acoustic wave cavity of the switch 12 in accordance with thepresent invention is formed at least in part integrally with thesubstrate 14, the switch 12 can be readily incorporated into a wall of ahousing for a device. As such, the switch 12 is extremely rugged anddoes not have any sealing problems. The acoustic wave switch 12utilizing a shear wave is insensitive to liquids and other contaminantson the touch surface 28 so that it is operable in the presence ofliquids and other contaminants. Moreover, the switch 12 is explosionproof. The high Q of the switch 12 enables a touch to be detected byextremely simple, inexpensive circuitry. It should be apparent thattouch detection circuits other than the oscillator circuit depicted inthe drawings can be used with the acoustic wave switch of the presentinvention. Moreover, the switch has a low enough power consumption to besuitable for portable or hand held devices. Although the switch 12 hasbeen described above with indicia 16 to identify the position of theswitch, by eliminating the indicia, a covert switch is provided.

Many modifications and variations of the present invention are possiblein light of the above teachings. For example, the cut-off frequency ofthe cavity region can be made less than the adjacent area surroundingthe cavity by other methods than described herein. Thus, it is to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as described hereinabove.

1. A feedback mechanism for an acoustic wave switch having a touchsensitive surface comprising: a deformable dome overlying the touchsensitive surface of the acoustic wave switch, the dome in an unactuatedposition being spaced from the touch sensitive surface of the switch;and an acoustic wave absorbing material disposed between the deformabledome and the touch sensitive surface such that in response to a forceacting on the dome, the dome deforms and contacts the absorbing materialand the absorbing material contacts the touch sensitive surface of theacoustic wave switch with sufficient pressure to actuate the acousticwave switch.
 2. A feedback mechanism for an acoustic wave switch asrecited in claim 1 wherein the acoustic wave absorbing material ismounted on a surface of the dome.
 3. A feedback mechanism for anacoustic wave switch as recited in claim 1 wherein the acoustic waveabsorbing material overlies the touch surface of the switch and isspaced from a surface of the dome in the unactuated position of thedome.
 4. A feedback mechanism for an acoustic wave switch having a touchsensitive surface comprising: an actuator overlying the touch sensitivesurface of the acoustic wave switch and an acoustic wave absorbingmaterial mounted on the actuator, the acoustic wave absorbing materialbeing spaced from the touch sensitive surface of the acoustic waveswitch when the actuator is in an unactuated position and the acousticwave absorbing material contacting the touch sensitive surface of theswitch actuating the acoustic wave switch in response to a force actingon the actuator to move the acoustic wave absorbing material intoactuating contact with the touch sensitive surface of the acoustic waveswitch.
 5. A feedback mechanism for an acoustic wave switch as recitedin claim 4 wherein the actuator is a deformable dome.
 6. A feedbackmechanism for an acoustic wave switch as recited in claim 5 wherein thedeformable dome is a truncated dome.
 7. A feedback mechanism for anacoustic wave switch as recited in claim 4 wherein the actuator includesa plunger extending through an aperture in a metal plate spaced from thetouch sensitive surface of the acoustic wave switch, the absorber beingmounted on a bottom surface of the plunger and further including atleast one magnet mounted on the plunger between the absorber and themetal plate to hold the actuator in the unactuated position.
 8. Afeedback mechanism for an acoustic wave switch having a touch sensitivesurface comprising: an actuator overlying the touch sensitive surface ofthe acoustic wave switch and an acoustic wave absorbing material mountedon the actuator, the acoustic wave absorbing material being spaced fromthe touch sensitive surface of the acoustic wave switch when theactuator is in an unactuated position and the acoustic wave absorbingmaterial contacting the touch sensitive surface of the switch actuatingthe acoustic wave switch in response to a force acting on the actuatorto move the acoustic wave absorbing material into actuating contact withthe touch sensitive surface of the acoustic wave switch, wherein theactuator includes a rocker having a pivot with a magnet mounted on therocker on a first side of the pivot to hold the actuator in anunactuated position and the magnet returns the actuator to theunactuated position when the force is removed.